[PATCH v10 06/12] powerpc: Add rethook support

Masami Hiramatsu
2022-03-08T11:10:00Z

Add rethook powerpc64 implementation. Most of the code has been copied from
kretprobes on powerpc64.

Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
---
Changes in v10:
- Add a dummy @mcount to arch_rethook_prepare().
---
arch/powerpc/Kconfig | 1 +
arch/powerpc/kernel/Makefile | 1 +
arch/powerpc/kernel/rethook.c | 72 +++++++++++++++++++++++++++++++++++++++++
3 files changed, 74 insertions(+)
create mode 100644 arch/powerpc/kernel/rethook.c

diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index b779603978e1..5feaa241fb56 100644
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig
@@ -229,6 +229,7 @@ config PPC
select HAVE_PERF_EVENTS_NMI if PPC64
select HAVE_PERF_REGS
select HAVE_PERF_USER_STACK_DUMP
+ select HAVE_RETHOOK if KPROBES
select HAVE_REGS_AND_STACK_ACCESS_API
select HAVE_RELIABLE_STACKTRACE
select HAVE_RSEQ
diff --git a/arch/powerpc/kernel/Makefile b/arch/powerpc/kernel/Makefile
index 4d7829399570..feb24ea83ca6 100644
--- a/arch/powerpc/kernel/Makefile
+++ b/arch/powerpc/kernel/Makefile
@@ -115,6 +115,7 @@ obj-$(CONFIG_SMP) += smp.o
obj-$(CONFIG_KPROBES) += kprobes.o
obj-$(CONFIG_OPTPROBES) += optprobes.o optprobes_head.o
obj-$(CONFIG_KPROBES_ON_FTRACE) += kprobes-ftrace.o
+obj-$(CONFIG_RETHOOK) += rethook.o
obj-$(CONFIG_UPROBES) += uprobes.o
obj-$(CONFIG_PPC_UDBG_16550) += legacy_serial.o udbg_16550.o
obj-$(CONFIG_SWIOTLB) += dma-swiotlb.o
diff --git a/arch/powerpc/kernel/rethook.c b/arch/powerpc/kernel/rethook.c
new file mode 100644
index 000000000000..a8a128748efa
--- /dev/null
+++ b/arch/powerpc/kernel/rethook.c
@@ -0,0 +1,72 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * PowerPC implementation of rethook. This depends on kprobes.
+ */
+
+#include <linux/kprobes.h>
+#include <linux/rethook.h>
+
+/*
+ * Function return trampoline:
+ * - init_kprobes() establishes a probepoint here
+ * - When the probed function returns, this probe
+ * causes the handlers to fire
+ */
+asm(".global arch_rethook_trampoline\n"
+ ".type arch_rethook_trampoline, @function\n"
+ "arch_rethook_trampoline:\n"
+ "nop\n"
+ "blr\n"
+ ".size arch_rethook_trampoline, .-arch_rethook_trampoline\n");
+
+/*
+ * Called when the probe at kretprobe trampoline is hit
+ */
+static int trampoline_rethook_handler(struct kprobe *p, struct pt_regs *regs)
+{
+ unsigned long orig_ret_address;
+
+ orig_ret_address = rethook_trampoline_handler(regs, 0);
+ /*
+ * We get here through one of two paths:
+ * 1. by taking a trap -> kprobe_handler() -> here
+ * 2. by optprobe branch -> optimized_callback() -> opt_pre_handler() -> here
+ *
+ * When going back through (1), we need regs->nip to be setup properly
+ * as it is used to determine the return address from the trap.
+ * For (2), since nip is not honoured with optprobes, we instead setup
+ * the link register properly so that the subsequent 'blr' in
+ * __kretprobe_trampoline jumps back to the right instruction.
+ *
+ * For nip, we should set the address to the previous instruction since
+ * we end up emulating it in kprobe_handler(), which increments the nip
+ * again.
+ */
+ regs_set_return_ip(regs, orig_ret_address - 4);
+ regs->link = orig_ret_address;
+
+ return 0;
+}
+NOKPROBE_SYMBOL(trampoline_rethook_handler);
+
+void arch_rethook_prepare(struct rethook_node *rh, struct pt_regs *regs, bool mcount)
+{
+ rh->ret_addr = regs->link;
+ rh->frame = 0;
+
+ /* Replace the return addr with trampoline addr */
+ regs->link = (unsigned long)arch_rethook_trampoline;
+}
+NOKPROBE_SYMBOL(arch_prepare_kretprobe);
+
+static struct kprobe trampoline_p = {
+ .addr = (kprobe_opcode_t *) &arch_rethook_trampoline,
+ .pre_handler = trampoline_rethook_handler
+};
+
+static int init_arch_rethook(void)
+{
+ return register_kprobe(&trampoline_p);
+}
+
+core_initcall(init_arch_rethook);